Composition and process for treating tinned surfaces

ABSTRACT

PCT No. PCT/US96/11535 Sec. 371 Date Jan. 21, 1998 Sec. 102(e) Date Jan. 21, 1998 PCT Filed Jul. 19, 1996 PCT Pub. No. WO97/04144 PCT Pub. Date Feb. 6, 1997This invention relates to a process comprising the steps of contacting a metal surface with an aqueous composition comprising water and specific amounts by weight of phosphate ions, condensed phosphate ions and water soluble polymer molecules of a specific general formula, separating the contacted metal surface from the aqueous composition, rinsing with water and heating.

TECHNICAL FIELD

This invention concerns novel waterbased compositions and methods forsurface treatment of metallic surfaces that are predominantly tin andmay be briefly denoted hereinafter simply as "tinned", particularly thesurfaces of tin-plated drawn-and-ironed (hereinafter usually abbreviated"DI") cans which have been formed by subjecting tin-plated steel sheetto drawing and ironing. Compositions and methods of the invention alsoimpart to the surfaces of such cans a low coefficient of surfacefriction, often referred to hereinafter simply as "-mobility", which isrequired for smooth and efficient mechanical conveying of the cans inhigh speed processing equipment in plants where such cans are lacquered,printed, and/or otherwise decorated on their surfaces.

BACKGROUND ART

Many liquid compositions, any of which hereinafter may be called "baths"for brevity, even though they may be used by spraying or other methodsof establishing contact than immersion, are known for the purpose oftreating tinned surfaces. The liquids disclosed, for example, inJapanese Patent Kokai H1-100281 are known as surface treatment liquidsfor tin-plated DI cans. These surface treatment liquids are chemicalfilm forming liquids for the treatment of metal surfaces which containfrom 1 to 50 grams/liter (hereinafter usually abbreviated as "g/L") ofphosphate ions, from 0.2 to 20.0 g/L of oxyacid ions, from 0.01 to 5.0g/L of tin ions and from 0.01 to 5.0 g/L of condensed phosphate ions,and in which the pH is from 2 to 6. Furthermore, surface treatmentagents which have further improved surface treatment operability havebeen disclosed in Japanese Patent Kokai H6-173024. It is possible bytreating tin-plated DI cans with these conventional chemical treatmentagents to form a phosphate film which has excellent corrosion resistanceof the surface of the tin-plated DI cans. However, there is a problem inthat no improvement of mobility is observed with these phosphate basedfilms. Furthermore, there has been a trend in recent years to reduce theamount of tin-plating on tin-plated DI cans, for reasons of economy, andsurface treatment which has much better corrosion resistance than in thepast is required for such lightly tin-plated DI cans.

On the other hand, if the outer surface of the cans has a high frictioncoefficient, in the can production process, slip failure between cansurfaces may occur during the conveyor transportation of a large numberof metal cans, so that the cans move sideways, and this leads toproblems with transportation. The transportability of the cans is aparticular problem when the cans are being moved into a printer. Hence,it is necessary to reduce the friction coefficient of the outer surfaceof the cans without having an adverse effect on the adhesion propertiesof the paint, printing ink(s) or lacquer which is to be coated on theouter surface of the can. The method disclosed in Japanese Patent KokaiS64-85292, for example, is known as a means of improving the mobility. Asurface treatment agent for metal cans which contains water solubleorganic materials selected from among phosphate esters, alcohols, mono-or poly-basic fatty acids, fatty acid derivatives and mixtures of thesematerials is used in this method. However, although an improvement inthe mobility is achieved by this method, there is a problem in thatthere is often inadequate improvement in corrosion resistance and/orpaint adhesion properties.

Furthermore, the methods disclosed in Japanese Patent Kokai S61-91369,Japanese Patent Kokai H1-172406, Japanese Patent Kokai HI-177379,Japanese Patent Kokai H1-177380, Japanese Patent Kokai H2-608 andJapanese Patent Kokai H2-609, for example, are known as methods for thesurface treatment of metals in which water soluble polymers are used,with a view to providing the metal surface with corrosion resistance andadhesive properties. With these conventional methods the metal surfaceis treated with a solution which contains derivatives of polyhydricphenol compounds. However, with these conventional methods it isdifficult to form a film which has adequate stability on the metalsurface, so that satisfactory corrosion resistance often is notobtained. Also, there is still a problem in that satisfactory paintadhesion is not always obtained even with the method of treatmentdisclosed in Japanese Patent Kokai H4-187782 which is an improved methodof treatment which includes the above-mentioned derivatives ofpolyhydric phenol compounds.

DISCLOSURE OF THE INVENTION Problems to Be Solved by the Invention

The present invention is intended to provide predominantly tin metalsurfaces with protective films which have excellent corrosion resistanceand paint adhesion properties and which also provide excellent mobility,to resolve the problems of the prior art as outlined above.

Summary of the Invention

It has been discovered that films which have excellent corrosionresistance and paint adhesion properties, and which also have markedlyimproved--mobility, can be formed on tin-plated DI cans by bringing asurface treatment bath which contains specified amounts of phosphateions, condensed phosphate ions and water soluble polymer of a specifiedstructure and which has been adjusted to a pH of 6.0 or below intocontact with the tin-plated DI can surfaces, and then rinsing thetreated surfaces with water and drying by heating. The invention isbased upon this discovery.

Details of the Invention, Including Preferred Embodiments Thereof

A composition according to the present invention for treating thesurface of tinned metal characteristically comprises, preferablyconsists essentially of, or more preferably consists of, water and, inparts by weight:

(A) from 0.5 to 30 parts of orthophosphate ions (hereinafter usuallydenoted simply as "phosphate ions", except when it is necessary todifferentiate them from condensed phosphate ions);

(B) from 0.1 to 10 parts of condensed phosphate ions; and

(C) from 0.1 to 20 parts of water-soluble polymer conforming with thefollowing general formula (I): ##STR1## in which each of X¹ and X²independently of each other and independently from one unit of thepolymer, said unit being defined as represented by a modification offormula (I) above in which the square brackets and the subscript n areomitted, to another unit of the polymer represents a hydrogen atom, a C₁to C₅ alkyl group, or a C₁ to C₅ hydroxyalkyl group; each of Y¹ and Y²independently of one another and independently for each unit of thepolymer represents a hydrogen atom or a moiety "Z" which conforms to oneof the following formulas (II) and (III): ##STR2## wherein each of R¹,R², R³, R⁴, and R⁵ in formulas (II) and (III) independently represents aC₁ to C₁₀ alkyl group or a C₁ to C₁₀ hydroxyalkyl group; the moiety Zbonded to any single aromatic ring in the polymer molecule may beidentical to or may differ from the moiety Z bonded to any other phenylring in the polymer molecule; and n represents a positive integer. Incomponent (C) as a whole, the average value for the number of Z moietiessubstituted on each phenyl ring in the polymer molecule, which may bereferred to hereinafter as "the average value for Z moietysubstitution", is from 0.2 to 1.0; and the average value of n, which maybe referred to hereinafter as "the average degree of polymerization", isfrom 2 to 50.

Compositions according to the invention as described above may be eitherworking compositions, suitable for directly treating tinned metalsubstrates, or they may be concentrate compositions, which are usefulfor preparing working compositions, usually by dilution of theconcentrate compositions with water, and optionally, adjustment of thepH of the resulting working composition. In a working composition, thetotal parts by weight of the composition preferably is 1000, when thethree necessary ingredients other than water in the composition arepresent in parts by weight as already specified above. For concentrates,the total number of parts by weight will normally be considerably lessthan 1000, in particular preferably, primarily for reasons of economy,not more than, with increasing preference in the order given, 500, 250,200, 150, 100, or 60 total parts by weight, when the three necessaryingredients other than water in the composition are present in parts byweight as already specified above.

A method according to the present invention for treating the surface oftinned metal characteristically comprises contacting the surface oftinned metal with a surface treatment bath containing a surfacetreatment composition as defined above according to the presentinvention, then rinsing the treated surface with water, and subsequentlydrying the surface by heating. Independently, in a method according tothe present invention, the bath preferably has a pH value of 6.0 orless, the total time of contacting the metal to be treated preferably isfrom 5 to 60 seconds, and the temperature during its contact with thetinned metal being treated preferably is from 35 to 65° C.

In this invention, phosphoric acid (i.e., H₃ PO₄) and sodium phosphate(i.e., Na₃ PO₄), for example, can be used to provide the phosphate ionsfor the water-based composition, but the system is not limited to theuse of these materials; any other water soluble salt or acid salt oforthophosphoric acid that does not act adversely to the objects of theinvention may be used, and any such salt is to be understood, for thepurpose of the preferences indicated below, as contributing its fullstoichiometric equivalent as orthophosphate ions to the concentrationthereof in any composition according to the invention, irrespective ofthe actual degree of ionization that may prevail in the composition.This phosphate ions content is preferably within the range from 0.5 to30 parts by weight, and most desirably within the range from 1 to 5parts by weight, with respect to from 0.1 to 20 parts by weight of thewater soluble polymers of formula (I). With a phosphate ions content ofless than 0.5 parts by weight, the reactivity of the treatment liquidwith the metal surface is low and a satisfactory film is not usuallyformed. Furthermore, although a good film is formed when the amount usedexceeds 30 parts by weight, the cost of the treatment liquid isincreased and this is disadvantageous economically.

Similarly, one or two or more types selected from among pyrophosphoricacid, tripolyphosphoric acid and tetrapolyphosphoric acid, and the saltsof all of these acids, can be used to provide the condensed phosphateions in a water-based composition of this invention, but the inventionis not limited to the use of these materials. Any water soluble sourceof any phosphate anions that contain at least two atoms of phosphoruseach may be used, and is to be understood for the purposes of thepreferences below as supplying its full stoichiometric equivalent ascondensed phosphate anions to the composition used according to theinvention, irrespective of the actual degree of ionization that existsin the composition. For example, pyrophosphoric acid (H₄ P₂ O₇), sodiumpyrophosphate (Na₄ P₂ O₇) and like compounds can be used to provide thepyrophosphate ions. The amount of condensed phosphate ions includedpreferably is from 0.1 to 10 parts by weight, and more preferably withinthe range from 0.5 to 3.0 parts by weight, with respect to from 0.1 to20 parts by weight of the water soluble polymers of formula (I). With acondensed phosphate ions content of less than 0.1 part by weight, theetching action of the treatment liquid obtained on the metal surface isweak, and a sufficiently strong film can not usually be formed in aneconomically realistic time. On the other hand, if the amount ofcondensed phosphate ions included exceeds 10 parts by weight, theetching action apparently becomes too strong and the film formingreaction is impeded.

In formula (I), X¹ and X² each independently represents a hydrogen atom,a C₁ to C₅ alkyl group or a C₁ to C₅ hydroxyalkyl group. In those caseswhere the alkyl group or hydroxyalkyl group has six or more carbonatoms, the polymer obtained is bulky and steric hindrance arises, sothat it is normally impossible to form a tight film which providesexcellent corrosion resistance.

In formula (I), Y¹ and Y² each independently represents a hydrogen atomor a Z group which can be represented by the formulas already given. Informula (II) and formula (III), R¹, R², R³, R⁴ and R⁵ each independentlyrepresents a hydrogen atom or one moiety selected from among the C₁ toC₁₀ alkyl moieties and the C₁ to C₁₀ hydroxyalkyl moieties. In thoseinstances where an alkyl moiety or hydroxyalkyl moiety has eleven ormore carbon atoms, a Z moiety which is obtained is too bulky, so thatthe film which is formed is coarse and its corrosion resistance isusually inadequate.

The average value of the substitution number of the aforementioned Zmoieties on each aromatic ring in the aforementioned polymer molecule isfrom 0.2 to 1.0. For example, with a polymer in which n is 10 (which hastwenty aromatic rings), the substitution number when there are ten Zmoieties substituted is 10/20=0.5. With an average Z moiety substitutionnumber of less than 0.2, the water solubility of the polymers is usuallyinadequate and the stability of the treatment liquid becomes poor. Onthe other hand, when the Z moiety substitution number exceeds 1.0, thewater solubility of the polymer obtained usually is excessively high, sothat a film can not be formed satisfactorily.

The amount of polymer of formula (I) included in a water-basedcomposition of this invention is set within the range from 0.1 to 20parts by weight as solids with respect to from 0.5 to 30 parts by weightof phosphate ions. This is because with less than 0.1 part by weight itis difficult to form a film in a stable manner on the metal surfacewhile, if the amount included exceeds 20 parts by weight, the cost ofthe treatment liquid is high and this is a problem in economic terms.

The average degree of polymerization is from 2 to 50; if this value isless than 2, there is little or no improvement in corrosion resistancefrom the film which is obtained. Furthermore, if the average degree ofpolymerization exceeds 50, the stability of the water-based compositionwhich is obtained is low, and this leads to problems in practical use.

In a process according to the invention, the pH of the surface treatmentliquid which contains the aforementioned water-based composition forsurface treatment purposes must be adjusted to 6.0 or below, because ifit exceeds 6.0 a precipitate is liable to form, and the life of theliquid is therefore shortened. The pH is preferably in the range from3.0 to 4.0. The pH of the treatment liquid can be adjusted using acidssuch as phosphoric acid, nitric acid and hydrochloric acid or alkaliessuch as sodium hydroxide, sodium carbonate and ammonium hydroxide.Moreover, hydrofluoric acid may be used as a pH adjusting agent in thoseinstances where there is no problem with effluent treatment, such aswhere adequate pollution abatement treatment equipment already existsand can be operated at an economically acceptable cost.

Also, there are instances in which, when the tin ions that have beendissolved out from the metal surface mix with the treatment liquid, thepolymer and tin form a complex and a precipitate is formed. In such acase, a tin chelating agent may advantageously be added to the treatmentliquid. Ethylene diamine tetra-acetic acid, 1,2 cyclohexene diaminetetractic acid, triethanolamine, gluconic acid, heptogluconic acid,oxalic acid, tartaric acid, malic acid and organophosphonic acids, forexample, can be used as tin chelating agents, but the agent used is notlimited only to these materials.

Moreover, oxidizing agents may be included in the treatment liquid witha view to accelerating the coating forming reaction. No narrowlimitation is imposed upon the type of oxidizing agent, and hydrogenperoxide, for example, can be used.

Also, there are instances when problems arise with foaming of thetreatment liquid when a surface treatment liquid which contains awater-based composition for surface treatment purposes of this inventionis being used for the spray treatment of tin-plated DI can surfaces.Whether or not foaming occurs is generally dependent to a great extenton the conditions of the apparatus, but in those instances where theoperating conditions can not be modified to stop foaming, ananti-foaming agent may advantageously be added to the treatment liquid.No narrow limitation is imposed upon the anti-foaming agent, and anysuitable agent which does not adversely affect adhesiveness of paint inany subsequent painting operation may be selected.

A polymer composition according to the present invention may contain apreservative or antimold agent. These function to inhibit putrefactionor mold growth when the surface treatment bath is used or stored at lowtemperatures. Hydrogen peroxide is a specific example in this regard.

In the preparation of a surface treatment liquid of this invention,first the phosphate ions source(s) and condensed phosphate ionssource(s) are dissolved in a suitable amount in water in accordance withthe aforementioned formulation, and the solution is stirred adequately.Next, the water soluble polymer of formula (I) is added to the solutionand a surface treatment liquid according to the invention is obtained.Any of the optional ingredients noted above may be added subsequently.

The film which is formed by a surface treatment liquid of this inventionis an organic-inorganic composite film which has phosphate(s) andpolymer of formula (I) as the main components. The film formationprocess is hypothesized, without any intent to limit the invention, tooccur as follows: Initially the tinned substrate is etched by thephosphate ions and condensed phosphate ions, so that a local rise in pHoccurs at the interface between the treatment liquid and the metalsurface, causing metal phosphate(s) to precipitate on the surface. Thephenol moieties and amino moieties of the water soluble polymer which isused in the invention can have a chelating action, so that a type ofcoordination compound can be formed by the bonding of this material onthe fresh substrate surface which has been formed by the etching. Anorganic-inorganic composite film is formed by these two simultaneousreactions (the precipitation of phosphate and the formation ofcoordination compounds). Polymer-metal coordination compound appears tobe formed more easily when condensed phosphate ions are present in thereaction system and, as a result of this, it is possible to form anorganic-inorganic composite film on the metal surface in a stable mannerover a wide pH range.

Furthermore, it appears to be possible to polymerize further the polymeron the surface by heating the film which has been formed. Heating of thefilm is effective in instances when an especially high degree ofcorrosion resistance is required. Heating for a time of at least 1minute at a temperature of about 200° C. is preferred for this purpose.

In a process according to this invention, the surface treatment liquidis preferably used in a process sequence such as that indicated below.

(1) Degreasing (generally with a weakly alkaline detergent)

(2) Water Rinse

(3) Film Forming Treatment

Treatment Temperature: 35-65° C.

Treatment Method: Spray

Treatment Time: 5-60 seconds

(4) Water Rinse

(5) Rinsing with Deionized Water

(6) Drying

In the method of this invention the surface treatment liquid ispreferably heated to a temperature of from 35 to 65° C. during use. Theheated surface treatment liquid is brought into contact with the surfaceof the tin-plated DI can. The contact is preferably achieved byintermittent spraying, with each two consecutive periods of sprayingseparated by an interspraying time interval in which spraying isdiscontinued, because it has been found that a rise in pH in thevicinity of the interface between the metal surface and the treatmentliquid is unlikely to continue to exist when the treatment liquid isbeing sprayed continuously, and under these conditions, the film doesnot form satisfactorily.

Because the interspraying time intervals are preferably only a fewseconds long, and preferably no rinsing or other method of forciblyremoving the previously applied aqueous liquid coat-forming compositionfrom the substrate surface is utilized during these intersprayingintervals, contact between the substrate surface and this surfacetreatment liquid normally continues during the interspraying intervals.Accordingly, the "total contact time" of the treatment liquid with thesubstrate surface in a process according to the invention is defined toinclude any intervals between beginning the first forced contact andending the last forced contact between the substrate being treated andthe treatment liquid, even when these first and last forced contacts areinterrupted by intervals during which contact is not forced. This totalcontact time is preferably within the range from 5 to 60 seconds. With atotal contact time of less than 5 seconds, the treatment liquid usuallydoes not react adequately with the metal surface, so that a film whichhas excellent corrosion resistance is not formed. If the total contacttime exceeds 60 seconds, there is generally no increase in protectivevalue of the coating formed, and costs are higher.

The invention is illustrated in greater detail below through workingexamples, and its benefits may be further appreciated by contrast withthe comparison examples. The individual surface treatment bathcomponents and surface treatment methods are respectively described inthe working and comparative examples.

EXAMPLES Evaluation Methods

(1) Corrosion Resistance

The corrosion resistance of the treated tin-plated DI cans was assessedby means of a red-rust test and the iron exposure value (hereinafterusually abbreviated as "IEV"). In the red-rust test, the treatedtin-plated DI cans were immersed in hot tap water at 65° C. for 30minutes and the extent of rust formation was evaluated by observation.The absence of rust was indicated by "++", partial rusting was indicatedby "+" and full surface rusting was indicated by "X". Furthermore,corrosion of the tin-plated DI cans in many cases starts at the exposediron parts produced in the DI process, so that the quality of coveringby the film can be evaluated by measuring the exposed iron value Themeasurement of the IEV of the tin-plated DI cans was carried out inaccordance with the method described in U.S. Pat. No. 4,332,646. Ingeneral, DI cans have a better corrosion resistance as the IEV valuefalls, and the corrosion resistance is generally good if the IEV valueis less than 100.

(2) Paint Adhesion

Epoxy-urea based paint for cans was coated onto the surface of a treatedcan to a paint film thickness of from 5 to 7 μm and baked for 4 minutesat 215° C. Then the can was cut in the form of a strip measuring 5×150mm and a sample was obtained by hot pressing a polyamide film onto thisand peeling off the film using the 180° peel test method, and the paintadhesion was assessed by the peel strength at this time. Hence, thepaint film adhesion was better as the peel strength increased. Ingeneral, the material is good if the peel strength is greater than 4.0kilograms of force per 5 millimeters of width (hereinafter usuallyabbreviated as "kgf/5 mm").

(3) Mobility

The mobility of the cans was evaluated by measuring the static frictioncoefficient of the outer surface of the cans. Hence, better mobility isobtained with a lower static friction coefficient. In general, themobility of the cans is adequate if the static friction coefficient isless than 1.0.

Example 1

Tin-plated DI cans which had been made from #25 tin plate were degreasedby means of a 40 second spray treatment with a 1% aqueous solution ofalkali based degreasing agent (named FINECLEANER® 4361A, manufactured byNihon Parkerizing Co.) at 60° C. Then they were cleaned by rinsing withwater, after which they were sprayed five times for a period of 2seconds each with 5 second intervals, for a total contact time of 30seconds, using Surface Treatment Liquid (1), with the compositionindicated below, which had been heated to a temperature of 60° C. Next,they were rinsed with tap water and then sprayed for 10 seconds withdeionized water which had a specific resistance value of at least3,000,000 ohm·centimeters, and then they were dried for 2 minutes in ahot forced air drying oven at 180° C.

Surface Treatment Liquid (1)

75% Phosphoric acid (i.e., H₃ PO₄): 10.0 g/L (PO₄ ³⁻ : 7.2 g/L)

Sodium pyrophosphate (i.e., Na₄ P₂ O₇.10H₂ O): 3.0 g/L (P₂ O₇ ⁴⁻ : 1.2g/L)

Polymer (1)--solids part: 2.0 g/L

pH 4.0 (Adjusted with sodium hydroxide)

Water Soluble Polymer (1) was according to formula (I) when: the averagevalue of n=5; each of X¹ and X² represents a hydrogen atom; each of Y¹and Y² represents a --CH₂ N(CH₃)₂ group or hydrogen atom; and theaverage Z moiety substitution number=0.25.

Example 2

After cleaning of the tin-plated DI cans under the same conditions asdescribed in Example 1, the cans were sprayed twice for 8.5 seconds eachwith a 3 second interval for at total contact time 20 seconds, usingSurface Treatment Liquid (2) with the composition indicated below, whichhad been heated to a temperature of 60° C. After treatment, the DI canswere rinsed and dried under the same conditions as in Example 1.

Surface Treatment Liquid (2)

75% Phosphoric acid (i.e., H₃ PO₄): 10.0 g/L (PO₄ ³⁻ : 7.2 g/L)

Sodium pyrophosphate (i.e., Na₄ P₂ O₇.10H₂ O): 3.0 g/L (P₂ O₇ ⁴⁻ : 1.2g/L)

Polymer (1)--solids part: 0.4 g/L

pH 3.0 (Adjusted with sodium carbonate)

The water soluble polymer was the same as that used in Example 1.

Example 3

After cleaning of tin-plated DI cans under the same conditions asdescribed in Example 1, the cans were sprayed four times for 3 secondseach with 1 second intervals for a total contact time of 15 seconds,using Surface Treatment Liquid (3) with the composition indicated below,which had been heated to a temperature of 35° C. After treatment, the DIcans were rinsed and dried under the same conditions as in Example 1.

Surface Treatment Liquid (3)

75% Phosphoric acid (i.e., H₃ PO₄): 20.0 g/L (PO₄ ³⁻ : 14.4 g/L)

Sodium pyrophosphate (i.e., Na₄ P₂ O₇.10H₂ O) 6.0 g/L (P₂ O₇ ⁴⁻ : 2.4g/L)

Polymer (1)--solids part: 8.0 g/L

pH 6.0 (Adjusted with sodium hydroxide)

The water soluble polymer was the same as that used in Example 1.

Example 4

After cleaning of tin-plated DI cans under the same conditions asdescribed in Example 1, the cans were sprayed twice for 2 seconds eachwith a 2 second interval (total contact time 6 seconds) using SurfaceTreatment Liquid (4) with the composition indicated below, which hadbeen heated to a temperature of 65° C. After treatment, the DI cans wererinsed and dried under the same conditions as in Example 1.

Surface Treatment Liquid (4)

75% Phosphoric acid (i.e., H₃ PO₄): 1.5 g/L (PO₄ ³⁻ : 1.1 g/L)

Sodium pyrophosphate (i.e., Na₄ P₂ O₇.10H₂ O): 5.0 g/L (P₂ O₇ ⁴⁻ : 2.0g/L)

Polymer (1)--solids part: 4.0 g/L

pH 2.5 (Adjusted with nitric acid)

The water soluble polymer was the same as that used in Example 1.

Example 5

After cleaning of tin-plated DI cans under the same conditions asdescribed in Example 1, the cans were sprayed four times for 4.5 secondseach with 4 second intervals for a total contact time of 30 seconds,using Surface Treatment Liquid (5) with the composition indicated below,which had been heated to a temperature of 60° C. After treatment, the DIcans were rinsed and dried under the same conditions as in Example 1.

Surface Treatment Liquid (5)

75% Phosphoric acid (i.e., H₃ PO₄): 30.0 g/L (PO₄ ³⁻ : 21.6 g/L)

Sodium tripolyphosphate (i.e., Na₅ P₃ O₁₀): 1.2 g/L (P₃ O₁₀ ⁵⁻ : 0.8g/L)

Polymer (1)--solids part: 2.0 g/L

pH 3.5 (Adjusted with sodium hydroxide)

The water soluble polymer was the same as that used in Example 1.

Example 6

After cleaning of tin-plated DI cans under the same conditions asdescribed in Example 1, the cans were sprayed twice for 7.5 seconds eachwith a 5 second interval for a total contact time of 20 seconds, usingSurface Treatment Liquid (6) with the composition indicated below, whichhad been heated to a temperature of 60° C. After treatment, the DI canswere rinsed and dried under the same conditions as in Example 1.

Surface Treatment Liquid (6)

75% Phosphoric acid (i.e., H₃ PO₄): 10.0 g/L (PO₄ ³⁻ : 7.2 g/L)

Sodium pyrophosphate (i.e., Na₄ P₂ O₇.10H₂ O): 3.0 g/L (P₂ O₇ ⁴⁻ : 1.2g/L)

Polymer (2)--solids part : 2.0 g/L

pH 5.0 (Adjusted with sodium hydroxide)

Water Soluble Polymer (2) was a polymer according to formula (I) when:the average value of n=5; each of X¹ and X² represents a --C₂ H₅ moiety;each of Y¹ and Y² represents a --CH₂ N(CH₂ CH₂ OH)₂ moiety or a hydrogenatom; and the average Z moiety substitution number=1.0

Example 7

After cleaning of tin-plated DI cans under the same conditions asdescribed in Example 1, the cans were sprayed five times for 2 secondseach with 5 second intervals for a total contact time of 30 seconds,using Surface Treatment Liquid (7) with the composition indicated below,which had been heated to a temperature of 60° C. After treatment, the DIcans were rinsed and dried under the same conditions as in Example 1.

Surface Treatment Liquid (7)

75% Phosphoric acid (i.e., H₃ PO₄): 10.0 g/L (PO₄ ³⁻ : 7.2 g/L)

Sodium pyrophosphate (i.e., Na₄ P₂ O₇.10H₂ O): 3.0 g/L (P₂ O₇ ⁴⁻ : 1.2g/L)

Polymer (3)--solids part: 2.0 g/L

pH 4.0 (Adjusted with sodium hydroxide)

Water Soluble Polymer (3) was a polymer according to formula (I) when:is the average value of n=2; each of X¹ and X² represents a --C₂ H₅moiety; each of Y¹ and Y² represents a --CH₂ N(CH₂ CH₂ CH₂ OH)₂ moietyor hydrogen atom; and the average Z moiety substitution number 0.6.

Comparative Example 1

After cleaning of tin-plated DI cans under the same conditions asdescribed in Example 1, the cans were sprayed five times for 2 secondseach with 5 second intervals for a total contact time of 30 seconds,using Surface Treatment Liquid (8) with the composition indicated below,which had been heated to a temperature of 60° C. After treatment, the DIcans were rinsed and dried under the same conditions as in the examples.

Surface Treatment Liquid (8)

75% Phosphoric acid (i.e., H₃ PO₄): 10.0 g/L (PO₄ ³⁻ : 7.2 g/L)

Polymer (1)--solids part: 2.0 g/L

pH 3.0 (Adjusted with sodium carbonate)

The water soluble polymer was the same as in Example 1.

Comparative Example 2

After cleaning of tin-plated DI cans under the same conditions asdescribed in Example 1 they were sprayed continuously for 30 secondswith no interruption, using the Surface Treatment Liquid (9) of whichthe composition is indicated below and which had been heated to atemperature of 60° C. After treatment, the DI cans were rinsed and driedunder the same conditions as in the examples.

Surface Treatment Liquid (9)

75% Phosphoric acid (i.e., H₃ PO₄): 1.0 g/L (PO₄ ³⁻ : 0.72 g/L)

Polymer (1)--solids part: 2.0 g/L

pH 7.0 (Adjusted with sodium hydroxide)

The water soluble polymer was the same as in Example 1.

Comparative Example 3

After cleaning of tin-plated DI cans under the same conditions asdescribed in Example 1, the cans were sprayed twice for 1 second eachwith a 2 second interval for a total contact time of 4 seconds, usingSurface Treatment Liquid (10) with the composition indicated below,which had been heated to a temperature of 60° C. After treatment, the DIcans were rinsed and dried under the same conditions as in the examples.

Surface Treatment Liquid (10)

75% Phosphoric acid (i.e., H₃ PO₄): 10.0 g/L (PO₄ ³⁻ : 7.2 g/L)

Sodium pyrophosphate (i.e., Na₄ P₂ O₇.10H₂ O): 1.0 g/L (P₂ O₇ ⁴⁻ : 0.4g/L)

Polymer (1)--solids part 0.05 g/L

pH 4.0 (Adjusted with sodium carbonate)

The water soluble polymer was the same as in Example 1.

Comparative Example 4

After cleaning of tin-plated DI cans under the same conditions asdescribed in Example 1, the cans were sprayed twice for 7.5 seconds eachwith a 5 second interval for a total contact time of 20 seconds, usingSurface Treatment Liquid (11) with the composition indicated below,which had been heated to a temperature of 60° C.. After treatment, theDI cans were rinsed and dried under the same conditions as in theexamples.

Surface Treatment Liquid (11)

95% Sulfuric acid (H₂ SO₄) 2.0 g/L (SO₄ ²⁻ : 1.9 g/L)

Sodium pyrophosphate (Na₄ P₂ O₇.10H₂ O) 1.0 g/L (P₂ O₇ ⁴⁻ : 0.4 g/L)

Polymer (1)--solids part: 0.05 g/L

pH 3.5 (Adjusted with sodium carbonate)

The water soluble polymer was the same as in Example 1.

Comparative Example 5

After cleaning of tin-plated DI cans under the same conditions asdescribed in Example 1, the cans were sprayed continuously for 30seconds using Surface Treatment Liquid (12) with the compositionindicated below, which had been heated to a temperature of 60° C. Aftertreatment, the DI cans were rinsed and dried under the same conditionsas in the examples.

Surface Treatment Liquid (12)

75% Phosphoric acid (i.e., H₃ PO₄): 1.0 g/L (PO₄ ³⁻ : 0.72 g/L)

Sodium pyrophosphate (i.e., Na₄ P₂ O₇.10H₂ O) 1.0 g/L (P₂ O₇ ⁴⁻ : 0.4g/L)

Polymer (4)--solids part: 2.0 g/L

pH 4.0 (Adjusted with sodium hydroxide)

Water Soluble Polymer (4) was a polymer according to formula (I) when:the average value of n=5; each of X¹ and X² represents a --C₂ H₅ moiety;each of Y¹ and Y² represents a --CH₂ SO₃ H moiety; and the average Zmoiety substitution number=0.6.

Comparative Example 6

After cleaning of tin-plated DI cans under the same conditions asdescribed in Example 1, the cans were sprayed five times for 2 secondseach with 5 second intervals for a total contact time of 30 seconds,using Surface Treatment Liquid (13) with the composition indicatedbelow, which was a surface treatment liquid as taught in Japanese PatentKokai H4-187782 and which had been heated to a temperature of 60° C.After treatment, the DI cans were rinsed and dried under the sameconditions as in the examples.

Surface Treatment Liquid (13)

75% Phosphoric acid (i.e., H₃ PO₄): 1.0 g/L (PO₄ ³⁻ : 0.72 g/L)

Sodium pyrophosphate (i.e., Na₄ P₂ O₇.10H₂ O): 1.0 g/L (P.sub. O₇ ⁴⁻ :0.4 g/L)

Polymer (5)--solids part: 2.0 g/L

pH 4.0 (Adjusted with sodium hydroxide)

Water-Soluble Polymer 5 had the following formula (IV): ##STR3##

Comparative Example 7

After cleaning of tin-plated DI cans under the same conditions asdescribed in Example 1, the cans were sprayed three times for 8 secondseach with 3 second intervals for a total contact time of 30 seconds,using Surface Treatment Liquid (14) with the composition indicatedbelow, which had been heated to a temperature of 60° C. After treatment,the DI cans were rinsed and dried under the same conditions as in theexamples.

Surface Treatment Bath 14

75% Phosphoric acid (i.e., H₃ PO₄): 1.0g/L (PO₄ ⁻³ : 0.72 g/L)

Sodium pyrophosphate (i.e., Na₄ P₂ O₇.10H₂ O): 1.0 g/L (P₂ O₇ ⁻⁴ : 0.4g/L)

Polymer 6 (solids part): 2.0 g/L

pH: 4.0 (adjusted with sodium hydroxide)

Water-Soluble Polymer 6, which is a resin described in Japanese PatentKokai Number Hei 2-608, had the following formula (V): ##STR4##

Comparative Example 8

After cleaning of tin-plated DI cans under the same conditions asdescribed in Example 1, the cans were sprayed five times for 2 secondseach with 5 second intervals for a total contact time of 30 seconds witha 3% aqueous solution of a commercial chemical coat-forming agent (namedPALFOS® K3482A, manufactured by Nihon Parkerizing Co.), which had beenheated to a temperature of 40° C. After treatment the cans were rinsedand dried under the same conditions as in Example 1.

The evaluation results for Examples 1 to 7 and Comparative Examples 1 to8 are reported in Table 1 below.

As is clear from the results shown in Table 1, with the productsobtained in Examples 1 to 7 where a water-based composition for surfacetreatment purposes and the method of surface treatment of this inventionhad been used, the corrosion resistance, adhesion properties andmobility were excellent. On the other hand, the products obtained inComparative Example 1 (which contained no condensed phosphate ions),Comparative Example 2 (which contained no condensed phosphate ions andwhere the pH was higher than 6), Comparative Example 3 (where the totalcontact time was less than 5 seconds), Comparative Example 4 (whichcontained no phosphate ions but contained sulfate ions instead),Comparative Examples 5 to 7 (in which the water soluble polymer wasdifferent from those of formula (I) according to the invention) andComparative Example 8 (which did not use a surface treatment liquid ofthis invention but another commercial chemical forming agent), wheresurface treatment liquids outside the scope of the invention were used,were unable to satisfy simultaneously the requirements of corrosionresistance, paint adhesion and mobility.

BENEFITS OF THE INVENTION

By using the water-based compositions and processes of this invention,excellent corrosion resistance of and paint adhesion to the surface oftinned substrates can be achieved, along with the excellent mobilitywhich is required to achieve smooth conveyor transportation of tinnedcans before painting or printing them. Also, the burden of effluenttreatment can be reduced, because the surface treatment liquids of thisinvention are essentially chrome free and fluorine free.

                  TABLE 1                                                         ______________________________________                                        Results of the Evaluations                                                    Example                                                                       or Com-                                                                       parison                                                                       Example Corrosion Resistance                                                  ("C Ex")                                                                              Red Rust          Peel Strength,                                                                         Coefficient of                             Number  Test     IEV      kgf/5 mm Static Friction                            ______________________________________                                        Example 1                                                                             ++       15       4.0      0.7                                        Example 2                                                                             ++       15       4.0      0.7                                        Example 3                                                                             ++       15       4.0      0.7                                        Example 4                                                                             ++       15       4.0      0.7                                        Example 5                                                                             ++       15       4.0      0.7                                        Example 6                                                                             ++       15       4.0      0.7                                        Example 7                                                                             ++       15       4.0      0.7                                        C Ex 1  X        100      2.0      1.0                                        C Ex 2  X        500      1.5      1.2                                        C Ex 3  X        500      2.0      1.2                                        C Ex 4  X        500      1.5      1.2                                        C Ex 5  X        500      1.5      1.2                                        C Ex 6  +        50       2.0      1.0                                        C Ex 7  X        500      1.5      1.2                                        C Ex 8  +        50       4.0      1.2                                        ______________________________________                                    

The invention claimed is:
 1. A process for treating a tinned metalsurface in order to form on said surface a corrosion protective, paintadherent coating, said process comprising steps of:(I) bringing themetal surface being treated into contact with an aqueous liquidcoat-forming composition having a pH of not more than 6.0 and comprisingwater and:(A) from 0.5 to 30 parts by weight of phosphate ions; (B) from0.1 to 10 parts by weight of condensed phosphate ions; and (C) from 0.1to 20 parts by weight of water-soluble polymer molecules conforming tothe following general formula (1): ##STR5## in which (i) each of X¹ andX², independently of each other and independently from one unit of thepolymer, which is defined as a part of the polymer that conforms toformula (I) above except that the square brackets and the subscript nare omitted, to another unit of the polymer, represents a hydrogen atom,a C₁ to C₅ alkyl group, or a C₁ to C₅ hydroxyalkyl group; (ii) each ofY¹ and Y², independently of one another and independently from one unitof the polymer to another, represents a hydrogen atom or a moiety "Z"that conforms to one of the following formulas (II) and (III): ##STR6##wherein each of R¹, R², R³, R⁴, and R⁵, independently of each other andindependently from one unit of the polymer to another, represents a C₁to C₁₀ alkyl group or a C₁ to C₁₀ hydroxyalkyl group; (iii) the moiety Zbonded to any single phenyl ring in the polymer molecule may beidentical to or may differ from the moiety Z bonded to any other phenylring in the polymer molecule; (iv) the average value over component (C)as a whole for the number of Z moieties substituted on each phenyl ringin the polymer molecule is from 0.2 to 1.0; and (v) n is a positiveinteger with an average value over component (C) as a whole from 2 to50, so as to convert the metal surface contacted to a coated metalsurface; (II) separating the coated metal surface formed in step (I)from the aqueous liquid coat-forming composition with which it wascontacted in step (I) and thereafter rinsing the coated metal surfacewith water to produce a rinsed coated metal surface; and (III) heatingthe rinsed coated metal surface sufficiently to dry said surface andform a dry coated metal surface.
 2. A process according to claim 1,wherein: the contacting of step (I) is initiated by spraying the aqueousliquid coat-forming treatment composition onto the metal surface for afirst spray period time; after the first spray period time, spraying ofthe aqueous liquid coat-forming treatment composition is discontinuedfor a first interspraying interval time; after the first intersprayinginterval time, spraying of the aqueous liquid coat-forming treatmentcomposition is resumed for a second spray period time; and, optionally,the second spray period time is followed by at least one additionalprocess step pair, each said process step pair consisting of anadditional interspraying interval time followed by an additional sprayperiod time; a sum formed by adding to one another the times of allspray periods and of all interspraying intervals being defined as "totalcontact time" for process step (I).
 3. A process according to claim 2,wherein the total contact time for process step (I) is from 5 to 60seconds, and the aqueous liquid coat-forming composition in step (I) hasa pH value from 3.0 to 4.0.
 4. A process according to claim 3, whereinthe temperature of the aqueous liquid coat-forming composition in step(I) is maintained between 35 and 65° C. during all spray periods, andthe aqueous liquid coat-forming composition in step (I) consists of 1000total parts by weight.
 5. A process according to claim 2, wherein thetemperature of the aqueous liquid coat-forming composition in step (I)is maintained between 35 and 65° C. during all spray periods, and theaqueous liquid coat-forming composition in step (I) consists of 1000total parts by weight.
 6. A process according to claim 5, wherein duringor after step (III), the metal surface and any coating thereon areheated to a temperature of at least 200° C. for a time of at least 1minute.
 7. A process according to claim 4, wherein during or after step(III), the metal surface and any coating thereon are heated to atemperature of at least 200° C. for a time of at least 1 minute.
 8. Aprocess according to claim 3, wherein during or after step (III), themetal surface and any coating thereon are heated to a temperature of atleast 200° C. for a time of at least 1 minute.
 9. A process according toclaim 2, wherein during or after step (III), the metal surface and anycoating thereon are heated to a temperature of at least 200° C. for atime of at least 1 minute.
 10. A process according to claim 1, whereinduring or after step (III), the metal surface and any coating thereonare heated to a temperature of at least 200° C. for a time of at least 1minute.
 11. A process according to claim 10, wherein, in the aqueousliquid coat-forming composition in step (I), components (A), (B), and(C) are present in amounts having a ratio by weight to one anotherwithin the range of {1 to 5 parts of phosphate ions}:{0.5 to 3 parts ofcondensed phosphate ions}:{0.1 to 20 parts, solids basis, of watersoluble polymer conforming to formula (I)}.
 12. A process according toclaim 9, wherein, in the aqueous liquid coat-forming composition in step(I), components (A), (B), and (C) are present in amounts having a ratioby weight to one another within the range of {1 to 5 parts of phosphateions}:{0.5 to 3 parts of condensed phosphate ions}:{0.1 to 20 parts,solids basis, of water soluble polymer conforming to formula (I)}.
 13. Aprocess according to claim 8, wherein, in the aqueous liquidcoat-forming composition in step (I), components (A), (B), and (C) arepresent in amounts having a ratio by weight to one another within therange of {1 to 5 parts of phosphate ions}:{0.5 to 3 parts of condensedphosphate ions}:{0.1 to 20 parts, solids basis, of water soluble polymerconforming to formula (I)}.
 14. A process according to claim 7, wherein,in the aqueous liquid coat-forming composition in step (I), components(A), (B), and (C) are present in amounts having a ratio by weight to oneanother within the range of {1 to 5 parts of phosphate ions}:{0.5 to 3parts of condensed phosphate ions}:{0.1 to 20 parts, solids basis, ofwater soluble polymer conforming to formula (I)}.
 15. A processaccording to claim 6, wherein, in the aqueous liquid coat-formingcomposition in step (I), components (A), (B), and (C) are present inamounts having a ratio by weight to one another within the range of {1to 5 parts of phosphate ions}:{0.5 to 3 parts of condensed phosphateions}:{0.1 to 20 parts, solids basis, of water soluble polymerconforming to formula (I)}.
 16. A process according to claim 5, wherein,in the aqueous liquid coat-forming composition in step (I), components(A), (B), and (C) are present in amounts having a ratio by weight to oneanother within the range of {1 to 5 parts of phosphate ions}:{0.5 to 3parts of condensed phosphate ions}:{0.1 to 20 parts, solids basis, ofwater soluble polymer conforming to formula (I)}.
 17. A processaccording to claim 4, wherein, in the aqueous liquid coat-formingcomposition in step (I), components (A), (B), and (C) are present inamounts having a ratio by weight to one another within the range of {1to 5 parts of phosphate ions}:{0.5 to 3 parts of condensed phosphateions}:{0.1 to 20 parts, solids basis, of water soluble polymerconforming to formula (I)}.
 18. A process according to claim 3, wherein,in the aqueous liquid coat-forming composition in step (I), components(A), (B), and (C) are present in amounts having a ratio by weight to oneanother within the range of {1 to 5 parts of phosphate ions}:{0.5 to 3parts of condensed phosphate ions}:{0.1 to 20 parts, solids basis, ofwater soluble polymer conforming to formula (I)}.
 19. A processaccording to claim 2, wherein, in the aqueous liquid coat-formingcomposition in step (I), components (A), (B), and (C) are present inamounts having a ratio by weight to one another within the range of {1to 5 parts of phosphate ions}:{0.5 to 3 parts of condensed phosphateions}:{0.1 to 20 parts, solids basis, of water soluble polymerconforming to formula (I)}.
 20. A process according to claim 1, wherein,in the aqueous liquid coat-forming composition in step (I), components(A), (B), and (C) are present in amounts having a ratio by weight to oneanother within the range of {1 to 5 parts of phosphate ions}:{0.5 to 3parts of condensed phosphate ions}:{0.1 to 20 parts, solids basis, ofwater soluble polymer conforming to formula (I)}.